Ethylene glycol is a chemical which has found wide use in industry. It is used, for example in the preparation of plasticizers for vinyl polymers and as a component in polyester fibers and antifreeze formulations. In view of its many uses, there is a need to find new and more economical methods for preparing ethylene glycol.
Proposed methods for making ethylene glycol involve the reaction of carbon monoxide with hydrogen in the presence of variously proposed catalyst systems at elevated temperatures and pressures. For example Belgium Pat. No. 793,086 and U.S. Pat. No. 3,940,432 describe the cosyntheses of ethylene glycol and methanol from mixtures of carbon monoxide and hydrogen using a complex rhodium catalyst. U.S. Pat. No. 3,833,634 describes the use of various other metals as catalysts but indicates that only rhodium and cobalt were effective in producing the ethylene glycol.
U.S. Pat. No. 4,013,700 discloses a process for producing polyhydric alcohols, their ether and ester derivatives by reacting oxides of carbon and hydrogen in the presence of a quaternary phosphonium cation and a rhodium carbonyl complex.
In U. S. Pat. No. 4,265,828, there is described a process for producing ethylene glycol wherein a ruthenium-containing compound is dispersed in a low melting quaternary phosphonium or ammonium base or salt. Here higher pressures, on the order of 430 atm. were used.
A bimetallic catalyst comprising ruthenium(III) acetylacetonate and rhodium(III) acetylacetonate is disclosed in U.S. Pat. No. 4,315,994. Both compounds are dispersed in a low melting quaternary phosphonium or ammonium base or salt at a pressure of 500 psi (34 atm) or greater and at a temperature of at least 150.degree. C. It was necessary to use pressures in the range of 4000-6000 psi (272-408 atm).
Another process for producing ethylene glycol is disclosed in U.S. Pat. No. 4,396,726 and comprises contacting a mixture of carbon monoxide and hydrogen with a catalyst system comprising a ruthenium-containing compound and a special manganese-containing compound, both dispersed in a low melting quaternary phosphonium compound.
Copper-based catalysts have been used in the commercial production of methanol from synthesis gas. One example is U.S. Pat. No. 4,342,838 which discloses a cluster compound of the formula L.sub.2 M.sub.2 Ru.sub.6 C(CO).sub.16, wherein M may be copper, for use in converting synthesis gas to methanol.
Some of these processes are limited by the nature and activity of the catalyst systems. Some such catalysts have limited solubility, poor selectivity, are expensive to prepare or would require extra expense in construction of commercial scale units.
It would be an advance in the art to provide a catalyst system for producing ethylene glycol wherein compounds less expensive than rhodium are used, moderate pressures are used which cut expenses of construction and the selectivities are comparable with those of other systems using higher pressures and more expensive catalyst compounds.